The powder metallurgy process
High quality and accuracy of details
The basic production process of a sintered part
RAW MATERIAL
Sintered products are always made from a ceramic or metallic powder. Metal powders can be both pure metal (iron, copper) and alloyed powders (bronze, brass, steel, etc.). There are powders of different nature (spongy, irregular, spherical, laminar) that give certain properties to the component.
MIX
The base powder is mixed with various alloying elements, depending on the desired composition of the final product (such as graphite, nickel, copper, etc.), with an organic solid lubricant (necessary for compacting the powder), and sometimes other specialised additives. Strict additive dosing controls to are critical in achieving the desired mechanical, physical and chemical characteristics.
STRUCTURE DESIGN
Discussion with the customer of the characteristics of strength, size, shape. Creation of documentation and forms for the production of parts. Sometimes existing CAD drawings are in place that we can work from.
CONSOLIDATION
During the pressing process, powder is compressed into moulds under high pressure, ranging from 200 to 1500 MPa, depending on the required final density. The shape of the part is almost finalised at this stage, though it has not yet achieved its full strength. Minimal waste is produced as the exact amount of powder needed is used, offering cost savings compared to other moulding methods. The compacted part, known as a "green part," is then removed from the mould and has a certain level of mechanical strength.
SINTERING
Sintering is a thermal process where the compacted part is heated below the melting point of the base metal for a specified time. The high temperature causes the particles to weld together and allows alloying elements to diffuse through solid-state diffusion. This process occurs in continuous furnaces at controlled rates and in a regulated atmosphere. Sintering temperatures range from 750 to 1300°C, depending on the material and desired properties. The result is a metal part with specific microporosity, high dimensional accuracy, and functional characteristics that meet component specifications.
CALIBRATION
Our agglomerated parts ensure high dimensional accuracy, which is further enhanced through a calibration or sizing process. This process improves both the dimensional accuracy and density of the parts, and can also enhance surface roughness. This minimises the need for expensive additional procedures often required in other moulding technologies.
FINISHING
We have various turning, milling and grinding machines for mechanical treatment.With these machines, we can finish parts by removing any excess material or polish according to requirements.
Additional operations
Applying additional operations to a sintered component allows one or more characteristics to be improved that cannot be obtained directly in the main process
Calibration (Re-calibration)
This process consists of re-compacting the part inside a rigid mold that has a symmetrical opposite shape to the part.
Size can have several purposes:
● Increased dimensional accuracy in diameter, reaching IT 5. Degree of compaction below 4%.
● Creation of relief geometric details that cannot be realized in a compacted part, or improvement of roughness.
● Sealing. The degree of compaction used is 7-10% and it is also known as minting. Density up to 7.6 g/cm3 is possible.Porosity seepage
Impregnation consists in filling the pores with a chemical product:
● Oil impregnation. The oil contained in the pores can act as a lubricant for the bearing-shaft contact, thus providing self-lubrication.
● Impregnation with plastic or resin ensures sealing. This operation is quite common as part preparation before coating.
● Copper impregnation, called Infiltration. It consists of sintering the part together with a copper plate pressed onto it. Copper melts during sintering and seeps into the pores with the help of capillaries. Infiltration is used to increase the mechanical strength and toughness of low-alloy sintered steels.Mechanical treatment (additional mechanical treatment)
Sintered components can sometimes be machined when a shape or tolerance is required that cannot be acquired by stamping. Sintered parts support all common machining operations, i.e. turning, milling, drilling, tapping, grinding, lapping, reaming, polishing, etc.
Removal of burrs
Burrs are removed either in groups (hammering, shot blasting, etc.) or individually (brushing, polishing, electrolytic removal of burrs, etc.). Mass deburring is sometimes used to ensure a uniform surface or very low roughness.
Cleaning
Cleaning operations are used to reduce or eliminate the amount of solid or liquid contaminants, that a part may contain. There are many methods, depending on the material, the type of contaminant and the required specifications.
Steam treatment
This is a thermal cycle of controlled oxidation of steel, carried out in continuous steam furnaces. A layer of magnetite forms on the surface of the part and porosity. Its application to the component increases compressive strength, seals porosity and improves corrosion resistance in the environment.
Heat treatment
Heat treatment is a thermal cycle that changes the properties of the material. They are usually used to increase the hardness and strength of the component. The main heat treatments of the surface or core are: hardening, cementation and carbonitriding. Induction hardening is used to increase the hardness in the local area of the part. Other possible treatment methods are ion nitriding, oxynitrocementing or annealing.
A special case is hardened components made from a special type of steel that is hardened in a sintering furnace during cooling.Coating
This is the deposition of material on the surface of the component, which changes the properties of the surface without changing the chemical composition of the base metal. Coatings are applied to protect against wear, friction or corrosion.
Sintered parts accept almost all common coatings, such as zinc plating, chrome plating, nickel plating, phosphating, metallization, non-stick coating (polytetrafluoroethylene - PTFE) and other special coatings.Connection with other parts
Sintered parts can be connected to other sintered parts or components made by other technologies. Typical joining methods are welding, brazing, sintering, fitting, gluing, riveting, lapping, etc.